Many applications which use mobile communication systems require a high level of reliability. Such applications include remote health monitoring, remote health-care, monitoring of large advanced systems, power grid management and other industry automation control etc. These applications may be bit-error sensitive or delay sensitive.
In order to provide a high level of reliability, it is common to provide backup paths as a protection against the failure of the main or regular path. Typically these backup paths are provided on a different Radio Access Technology (RAT), for example if Wi-Fi is used for the regular path, then a 3GPP backup path will be provided. Such an arrangement is typically provided using a multipath protocol such as Multi-Path Transmission Control Protocol (MPTCP), which has the facility to provide multiple paths across different RAT's, giving the high level of reliability required.
However, there are drawbacks to establishing and maintaining such backup paths. Such paths are typically used to transmit only control signalling to maintain the backup path, for example establishment, release and possible keep-alive signalling for the backup path, and are only occasionally associated with data traffic. It is also necessary to create both radio access network and core network level of connectivity to enable establishment and release of backup paths. One example is in relation to 3GPP Evolved Packet System (EPS) which comprises both LTE (E-UTRAN) radio access network and Evolved Packet Core (EPC) network. User Equipment (UE) that wants to establish a backup path, e.g. using MPTCP, needs to enter a so called “connected” state to enable communication towards an MPTCP-server via the EPS. The UE is normally in the “connected” state for a short while and then moves to an “idle” state. When the backup path is to be released, the UE needs to again enter the “connected” state to signal the release of the backup path. Therefore, a lot of signalling overhead may be introduced without any useful information being sent, resulting in additional load on different network nodes and increased interference on other signals. In some situations, for example, when there is high load on a network, it may be desirable to limit the backup paths that do not carry any traffic, for example by restricting their usage of network resources via connection admission control, by giving subflows associated with such paths a lower priority compared to other paths/subflows or by restricting their power.
In order to implement such restrictions, it is necessary for the networks to recognise which paths are backup paths. It is also beneficial to recognise when a UE has only backup paths in a particular radio access network. Two mechanisms exist in the prior art for identifying backup subflows. The first of these is the use of the “B” bit in the MPTCP header. The second is the use of deep packet inspection in the network to identify subflows in which little or no data is being transmitted. Both of these mechanisms require a radio level connection, together with associated core network level connectivity, and a backup path to be already setup before identification of the backup path/subflow can take place.